Digital communication systems typically include a mobile unit, which may be embodied in an analog or digital cellular telephone or any other portable communication device, and an infrastructure unit, which may be embodied in a cellular base station or any other suitable communication hardware. During operation, the mobile unit and the infrastructure unit exchange digital information using one of a number of communication protocols. For example, the mobile and infrastructure units may exchange information according to a time division multiple access (TDMA) protocol, a code division multiple access (CDMA) protocol or a global system for mobile communications (GSM) protocol. The details of the TDMA protocol are disclosed in the IS-136 communication standard, which is available from the Telecommunication Industry Association (TIA). The GSM protocol is widely used in European countries and within the United States. The details of the GSM protocol are available from the European Telecommunications Standards Institute. The details of the second generation CDMA protocol are disclosed in the IS-95 communication standard. Third generation CDMA standards are typically referred to as WCDMA (Wideband CDMA). The most prevalent WCDMA standards that are currently being developed are the IS-2000 standard, which is an evolution of the IS-95 protocol, and the uniform mobile telecommunication system (UMTS) protocol, which is an evolution of the GSM protocol.
The presence of TDMA, CDMA and GSM protocol-based infrastructure disposed in various geographic regions throughout, for example, the United States may require a mobile telephone to process information according to any one of the TDMA, CDMA or GSM formats at any given time. For example, near major metropolitan areas a mobile unit may need to exchange information with CDMA base stations. Conversely, in other areas, GSM base stations may be prevalent and a mobile unit would need to exchange information according to the GSM format in such locations.
Because of the geographic differences in the types of infrastructure, some mobile units are able to process information according to any one of the TDMA, CDMA and GSM formats. For such processing to take place, mobile units must be able to detect the presence of signals formatted according to any one of these formats. It is known to power up various portions of different hardware to detect the presence of the variously formatted signals. For example, while communicating with a CDMA base station, a mobile unit may power up its GSM receiver hardware to determine if a GSM signal is present. However, as will be readily appreciated, powering up various portions of hardware merely to detect the presence of a signal is costly in terms of mobile unit battery life and processing demands.